1. Field of the Invention
This invention relates generally to an antenna structure and, in particular, to dual-polarized radiating elements that can be excited via control networks to select any desired polarization in space and which are suitable for use in transmitting and/or receiving phased arrays.
2. Discussion of the Background Art
In radio frequency (RF) antenna design the objective is to provide a design which is compatible with a feed network, can be manufactured using low cost batch techniques while providing broad bandwidth impedance match and pattern characteristics. Conventional notch antennas consist of a double-sided metalization on a dielectric substrate having the form of a flared slot. This conventional antenna includes a transition from a feed line to the notch antenna slot line which requires a slot line open circuit. In addition, the transition requires a short circuit through the circuit board.
A first notch antenna design is shown in U.S. Pat. No. 3,836,976 to Monser et al. The Monser et al patent discloses a phased array antenna which is comprised of a plurality of vertical radiating elements and a plurality of horizontal radiating elements which are arranged in a linear array and which are fixed to a back wall which forms a ground plane for the radiating elements. A drawback of this design is non-coincident phase centers of the vertical and horizontal elements. A second drawback of this design is caused by the ground plane which causes large reflections of incident energy and can be detrimental in some applications.
A second antenna design using notch antenna elements is shown in U.S. Pat. No. 4,978,965 to Mohuchy. The Mohuchy patent discloses a dual polarized radiating element composed of a notched radiator and a dipole radiator interlocked and orthogonal to each other. The described element has coincident phase centers and is backed by a structural absorber and solves the mechanical crossover problem with the feed network. A drawback of this design is that the two polarizations have different radiating elements with different performance qualities, which can be detrimental in certain applications.
There remains a need in the art for a dual-polarization radiator with orthogonal elements having coincident phase centers, wherein the orthogonal elements have about the same element pattern shape and performance characteristics, and wherein the radiators can be easily manufactured and assembled into a variety of phased array configurations.
An object of the present invention is to provide a dual-polarization radiator with orthogonal radiating elements which can be combined through an RF device with other similarly constructed radiators into a variety of phased array configurations compatible with at least one of wide bandwidth applications, wide scan-angle applications, microstrip circuitry, low cost batch fabrication, and coincident phase centers.
Specifically, an inventive dual-polarization radiator includes two dual planar notch radiating elements interlocked and orthogonal to each other. The radiating elements are preferably mounted on a ground plane covered by a structural absorber. Similarly constructed elements, when placed in an array, preferably have conductive xe2x80x9cbridgesxe2x80x9d placed between them shorting the elements to each other thus eliminating spurious resonances and element pattern distortion at higher frequencies. By dual planar notch is meant two notch antennas on one board, preferably in equal phase and magnitude. The feed system preferably includes a microstrip power divider and tapered impedance transformer.
The notched radiating elements are preferably fabricated from a dielectric material carrier or substrate which has exterior metallized regions to provide the respective radiating configurations and an exterior excitation means for exciting the respective radiating elements with energy from an RF device or for receiving incident RF energy.
Some of the advantages of this inventive dual-polarization radiatior include ease in array assembly due to the microstrip nature of the radiating elements and coincident phase centers using similar radiating elements that provide similar impedance and pattern performance for each polarization. The radiator can also improve the low frequency performance of an antenna array.